The present invention relates to a medical laser knife device.
In a laser knife device, a laser beam of 10.6 micron wavelength emitted by a CO.sub.2 laser is used to effectively break, remove or cut body tissue. The reason for the use of such a laser beam is that body tissue is made up of 75 to 90% water, water absorbs effectively infrared rays having a wavelength greater than 2.5 microns, and a CO.sub.2 laser beam has an extremely high energy conversion efficiency.
In a laser knife device of this general type, the laser beam emitted from the laser device is introduced through a multiarticulation type flexible light conducting device called "a manipulator" to a focusing lens provided at the end of the manipulator. The laser beam is focused by the focusing lens to obtain a very high energy density and the laser beam thus focused is applied to a desired part of the body to generate a high temperature of 1,500.degree. to 1,600.degree. C. momentarily to cut designated body tissue. Upon application of the laser beam, capillary vessels smaller than about 0.7 mm in diameter are automatically sealed and accordingly an operation can be achieved with little or no bleeding. On the other hand, if the part to be operated on is intricate anatomically, it is often required to cut or coagulate a part of tissue which is covered by lymph without evaporating the lymph. A specific example of this will be described.
The cochlear duct forming a part of the inner ear of a human being is located inside the temporal bone. In the cochlear duct, a membranous labyrinth is formed along the modiolus where the auditory sense cells are located. If the auditory sense cells become abnormal, whole or partial deafness or continuous tinnitus can result. In order to cure tinnitus, an operation of breaking or coagulating a part of the auditory sense cells on the membranous labyrinth has been performed by using a focused ultrasonic beam. However, in many cases it has been difficult to completely cure the tinnitus.
The use of a laser knife for such an operation is effective. In this case, an operating technique is employed in which a thin laser beam (hereinafter referred to as "an operating light beam" when applicable) is applied from near the bone window of the inner ear, namely, the round window which is located behind and below the tympanic cavity. First, a minute hole is cut in the bone window to allow the operating light beam to enter the cochlear duct through the minute hole as a result of which the operating light beam is applied through the lymph layer in the outer lymph space around the auditory sense cells. However, since lymph is substantially made up of water, the lymph is instantly evaporated by the operating light beam as a result of which the pressure is in the cochlear duct is abruptly increased which can, at worst, break the entire cochlear duct.
Accordingly, an object of the invention is to provide a laser knife device in which the above-described difficulties accompanying a conventional laser knife device have been effectively eliminated.